Saffir-Simpson Hurricane Wind Scale

The Saffir-Simpson Hurricane Wind Scale ranks North Atlantic and Northeast Pacific hurricanes in five categories by maximum sustained wind, averaged over one minute at ten meters above ground. Katrina made landfall in Louisiana on August 29, 2005 as a Category 3. The surge it drove onto the Mississippi coast and the failure of the New Orleans levees still made it the largest insured loss on record at the time. The scale dates from the early 1970s, the work of Herbert Saffir, an engineer, and Robert Simpson, then director of the US National Hurricane Center (NHC). It originally blended wind, central pressure and surge height. Since 2010 the NHC has kept only the wind, under the name Saffir-Simpson Hurricane Wind Scale, and the thresholds were adjusted in 2012. Category 1 starts at 74 mph (119 km/h), Category 3 at 111 mph (178 km/h), Category 5 at 157 mph (252 km/h). From Category 3 up, it counts as a major hurricane. Western Pacific typhoons and Indian Ocean cyclones are rated on other scales, with other wind-averaging periods. The market uses it as shorthand: a vendor's loss release or a cat bond market update quotes the category at landfall. Models do not take it as an input; the hazard module works from central pressure, radius of maximum winds and forward speed. A practitioner's caveat: the category measures neither size, nor rain, nor surge. Harvey, a Category 4 when it came ashore in Texas in late August 2017, did most of its damage through rainfall over Houston. Sandy, no longer a hurricane when it made landfall on October 29, 2012, did its damage through seawater.